1. Field of the Invention
This invention relates to a device for testing an electrical connection, and more particularly to a device for testing strength of individual connections in a wiring board, such as a printed wiring board, carrying semiconductor circuit elements mounted thereon.
The invention specifically relates to detection of faulty solder connections, such as those of metallic leads of parts, such as semiconductor circuit elements or packages, to the metal plate of a wiring board.
A test method using the device of the invention is very effective in checking the quality of solder connections in high-density parts, such as packages of semiconductor tips and flat packages of IC (integrated circuit), where inspection by sight and by finger touch is difficult to perform, and image information processing is hardly applicable.
The invention is based on laser-assisted instrumentation and on techniques using the application of photo-thermo elastic wave generation and the application of optical vibration probing.
2.Description of the Prior Art
Heretofore, no reliable test method has been available to check faulty solder connections in printed wiring boards carrying semiconductor elements. Various methods have been tried, such as a visual inspection method, an image information processing method, and a method using laser beam reflection peculiar to smooth surface of solder wetting, but no reliable and accurate criteria for determination of faulty soldering have been developed yet for practicable inspection of connection formation.
On the other hand, in the field of instrumentation optics using laser beams, a number of research reports have been published in relation to generation of photo-thermo strain and elastic wave caused thereby: for instance, "measurement of rate of thermal diffusion" by G. Rousset et al, Journal of Applied Physics 54, 2383 (1983); "Non-destructive Inspection of Laminar Material" by G. Rousset et al, Journal of Applied Physics 57, 4396 (1985), P. Cielo et al, Applied Optics 25, 1327 (1986); and "Detection of Defects in Thin plate sample" by K. Hane, T. Kanie, S. Hattori, Applied Optics 27, 386 (1988). However, there have been no reports which concern application of laser beams to detection of faulty soldering or which refer to any possibility of such application.